Inside the mouth of every child is a terrifying double row of teeth. Not that you'd ever know it — muscle, skin and bone prevent most of us from ever catching a glimpse of this extra dentition. Here's your chance to get a close-up look at what lies beyond the gum line.

On some level, most people probably recognize that a child's erupting permanent teeth have to be situated more or less right on top of their smaller predecessors, in order to dissolve their roots and ultimately replace them (a process known as exfoliation).

What many fail to appreciate, however, is just how little room there is for exfoliation to take place. This picture [click for hi-res], taken by photographer Stefan Schäfer at the Hunterian Museum in London, reveals several permanent teeth crammed into a space so small, it almost looks like they're burrowing outward in a bid to escape from the skull entirely — the front teeth via the eye and nasal cavities, the lower teeth by way of the jawline.

Stare at it too long, in fact, and the skull's primary teeth almost start to resemble a set of pharyngeal jaws. Wonderful. Now I'll never be able to look at a child again without thinking about xenomorph dentition. Biology: Not only is it fascinating, it's also high-octane nightmare fuel.